1. Field of the Invention
The present invention relates to a plasma processing apparatus such as a plasma etching apparatus having a driving control section.
2 Description of the Related Art
In a plasma etching apparatus, a control section send a driving control signal serving as a digital ON/OFF signal to various driving units on the basis of signals from various sensors arranged in a plasma processing section, such that the driving units of the apparatus are controlled. This control section has a host CPU (Central Processing Unit) at a position separated from the plasma processing section, and various signals are transmitted/received between the CPU and the various sensors and driving units. That is, signals are transmitted from the various sensors to the host CPU, and on the basis of these signals, the host CPU supplies control signals to the driving units. In general, digital signals are parallelly output from the host CPU to the driving units, i.e., units to be controlled, through an I/O port.
In a plasma processing apparatus such as a plasma etching apparatus, there are a large number of parts to be digital-controlled, i.e., about 200 points in the output section and about 100 points in the input section. For this reason, when conventional parallel transmission is performed, a very large number of cables must be arranged.
In a plasma processing apparatus, since a host CPU is normally separated from a plasma processing section, the plasma processing apparatus easily receives noise generated due to a ground level difference between the host CPU and the processing unit. In addition, the plasma processing apparatus is easily influenced by noise generated from a high-frequency power supply in the plasma processing section. When a digital signal is used, since the signal is determined as "1" or "0" depending on whether its signal level exceeds a predetermined threshold level from the ground level, the plasma processing apparatus is erroneously operated by noise. Therefore, a countermeasure, for example, sufficient shielding of cables, against noise must be performed.
However, since the plasma processing apparatus has a large number of cables as described above, it is substantially impossible that all the cables are sufficiently shielded to protect the cables from noise.